The metabolic status of encysted Artemia embryos under anoxic conditions has been studied by calorimetry. Previous work demonstrated a very low, but still measurable, source of metabolic heat (31 nW mg-1 dry mass) after 6 days of anoxia, attributed to the catabolism of small amounts of carbohydrate storage compounds and the unusual nucleotide diguanosine tetraphosphate. Our results indicate that the heat measured drops below the detection limits of our calorimeter (11 nW mg-1 dry mass) after 1.5 h of anoxia, in sharp contrast with previously published results. The possible sources of error that could explain this difference, and a re-evaluation of the metabolic status of cysts during anoxia, are discussed. We conclude that if the cysts are carefully protected from oxygen they become essentially ametabolic.

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